Phylogenetic structure of the Sphaeriinae, a global clade of freshwater bivalve molluscs, inferred from nuclear (ITS-1) and mitochondrial (16S) ribosomal gene sequences

The Sphaeriidae represent one of the primary molluscan radiations into freshwater environments. We have reconstructed phylogenetic relationships of the Sphaeriinae, a cosmopolitan sphaeriid subfamily, using variation in nuclear ribosomal first internal transcribed spacer (ITS-1) and mitochondrial large ribosomal subunit (16S) gene fragments. A total of 38 New World, Eurasian and Antipodean taxa were characterized, including all primary taxonomic groupings except for Neopisidium , and members of the sister clade Euperinae were employed as outgroups. Phylogenetic analyses of individual and combined (16S + ITS1) datasets all recovered a paraphyletic Pisidium and a derived clade of asynchronous brooding Sphaerium / Musculium taxa. Maximum parsimony as well as maximum likelihood analyses of combined data yielded largely congruent and well-resolved topologies, and robustly supported clades were utilized to revise current sphaeriine taxonomy. Instead of the traditionally accepted three cosmopolitan genera, Pisidium s.l. , Musculium , and Sphaerium , five major monophyletic lineages, Afropisidium , Odhneripisidium , Pisidium , Cyclocalyx and Sphaerium , were recognized at the generic level. In addition, a number of subgeneric level groups were recovered in Sphaerium : Herringtonium , Sphaerium s . s ., Sphaerinova , Amesoda , and Musculium , together with one unassigned species, S. transversum .     

Phylogenetic analysis based on the morphology of viviparous freshwater clams of the family Sphaeriidae (Mollusca, Bivalvia, Veneroida)

The cosmopolitan viviparous bivalves of the family Sphaeriidae (fingernail clams) comprise not only some of the smallest freshwater molluscs, but also an abundant and ecologically important group that often dominates benthic communities of springs, ponds and swamps. The origin from marine ancestors and their subsequent evolution in limnic environments, in particular the development of distinct reproductive modes including complex parental care repertoires, are largely unresolved. This paper presents the results of a phylogenetic analysis of 69 morphological characters from 57 taxa (54 representing sphaeriids throughout the distribution area plus three outgroups). The heuristic search resulted in 753 most-parsimonious trees of length 154 [consistency index (CI) = 0.682, retention index (RI) = 0.906, rescaled consistency index (RC) = 0.618]. Only Pisidium of the three traditionally regarded constituent genera is supported as a monophyletic group; Sphaerium and Musculium in their traditional deliminations are found to be paraphyletic. Instead, the analysis supports a clade comprising all species of Musculium plus Pisidium as suggested by previous morphology-based classifications. However, the shortest tree alternatively supporting a Sphaerium  +  Musculium clade suggested by molecular data is only one step longer. Some clades that correspond to the subgeneric divisions of the three traditionally recognized sphaeriid genera are supported. Exclusion is suggested of the taxon Euperidae ( Eupera and Byssodonta , both with ovo-viviparous species) from the true Sphaeriidae that then comprises all species with eu-viviparous reproductive mode, i.e. brooding and nourishing their embryos in specialized brood pouches in the gills. The implications for the reconstruction of the evolutionary history of Sphaeriidae and the availability of existing taxonomic names for the systematization suggested by the present analysis are discussed.     

Phylogenetic analysis of the Sphaeriidae (Mollusca: Bivalvia) based on partial mitochondrial 16s rDNA gene sequences

Abstract. We have constructed molecular phylogenetic trees for members of the Sphaeriidae in order to test proposed generic level relationships, and to reconstruct the evolutionary pattern of parental care, in this exclusively freshwater family of heterodont bivalves. An ∼480 nucleotide fragment of the mitochondrial large ribosomal subunit (16s rDNA) was sequenced for 4 corbiculid outgroups in addition to 19 sphaeriid ingroup taxa. Ingroup species were obtained from North and South America, Europe, and Australasia and included representatives of the main sphaeriid genera. Our analyses support four primary conclusions: 1) the Sphaeriinae are robustly monophyletic with respect to Eupera platensis ; 2) the genus Pisidium is paraphyletic and P. sterkianum is sister to the 17 other sphaeriine taxa in our dataset; 3) synchronous brooding is the ancestral reproductive pattern in the Sphaeriinae; 4) the sequential brooders form a clade in which Musculium taxa are monophyletic and nested among lineages of Sphueriunz. Our gene trees reveal an evolutionary progression in parental care complexity from the relatively simple pattern in the Euperinae, to the origin of brood sacs and of extraoogonial embryonic nutrition in the common ancestor of the Sphaeriinae, and ultimately to the development of sequential brooding in Sphaerium/Musculium taxa.     

6-Phosphogluconate Dehydrogenase (6PGD) Gene Duplication in Kalimeris (Asteraceae)

Abstract The genus Kalimeris with a diagnostic character of short or inconspicuous pappus consists of two sections, Asteromoea and Cordifolium. As a result of 6PGD isozyme analysis, sect, Asteromoea, including 2 × and poly-ploid taxa from 5 × to 8 ×, show similar cytosolic isozyme multiplicity and share a monomorphic locus. The data suggest that gene duplication of polyploid members was derived from a common ancestor. K. miqueliana, belonging to sect. Cordifolium. also possessed a gene duplication in 6PGD, though significant differences were detected in electrophoretic mobility between the sections. The occurrence of gene duplication in East Asian diploid Astereae leaves intact the validity of the allopolyploid-origin hypothesis of n= 9, which was rejected by Gottlieb (1981a) in American Astereae.     

Genomes,multiple origins,and lineage recombination in the Glycine tomentella (Leguminosae) polyploid complex: histone H3-D gene sequences

Relationships among the various diploid and polyploid taxa that comprise Glycine tomentella have been hypothesized from crossing studies, isozyme data, and repeat length variation for the 5S nuclear ribosomal gene loci. However, several key questions have persisted, and detailed phylogenetic evidence from homoeologous nuclear genes has been lacking. The histone H3-D locus is single copy in diploid Glycine species and has been used to elucidate relationships among diploid races of G. tomentella, providing a framework for testing genome origins in the polyploid complex. For all six G. tomentella polyploid races (T1-T6), alleles at two homoeologous histone H3-D loci were isolated and analyzed phylogenetically with alleles from diploid Glycine species, permitting the identification of all of the homoeologous genomes of the complex. Allele networks were constructed to subdivide groups of homoeologous alleles further, and two-locus genotypes were constructed using these allele classes. Results suggest that some races have more than one origin and that interfertility within races has led to lineage recombination. Most alleles in polyploids are identical or closely related to alleles in diploids, suggesting recency of polyploid origins and spread beyond Australia. These features parallel the other component of the Glycine subgenus Glycine polyploid complex, G. tabacina, one of whose races shares a diploid genome with a G. tomentella polyploid race.     

Molecular evidence of reticulate evolution in the subgenus Plantago (Plantaginaceae)

Polyploidization is a frequent evolutionary event in plants that has a large influence on speciation and evolution of the genome. Molecular phylogenetic analyses of the taxonomically complex subgenus Plantago were conducted to elucidate intrasubgeneric phylogenetic relationships. A nuclear-encoding single-copy gene, SUC1 (1.0-1.8 kb), was sequenced in 24 taxa representing all five sections of the subgenus Plantago and two taxa from subgenus Coronopus as the outgroup. Fifteen known polyploids and one putative polyploid were sampled to examine polyploid origins and occurrence of reticulate evolution by cloning and sequence analysis of SUC1. Phylogenetic relationships were estimated using maximum parsimony, neighbor-joining, and Bayesian analyses. For the first time, our analysis provides a highly resolved phylogenetic tree. Subgenus Plantago formed a well-supported monophyletic clade. In contrast, alleles from polyploid species were scattered across the whole SUC1 phylogenetic tree, and some independent allopolyploids originated from hybridization between distant lineages. One reason for this taxonomic complexity can be attributed to reticulate evolution within the subgenus Plantago. Our results also suggest the possibility of two independent long-distance dispersals between the northern and southern hemispheres.     

Nuclear DNA content in two Sphaeriidae species from Southern Chile (Bivalvia: Veneroida)

The family Sphaeriidae is a group of cosmopolitan freshwater clams that inhabit temporary and permanent fluvial and lacustrine environments around the world. In Chile, Sphaeriidae is represented by 11 species belonging to the genera Musculium, Pisidium and Sphaerium. In this study, the nuclear DNA content (or 2C-value) of Musculium argentinum (d’Orbigny, 1835) and Pisidium llanquihuense Ituarte, 1999 was estimated for the first time. Musculium argentinum showed a 2C-value of 3.7?±?0.38?pg, whereas P. llanquihuense showed a 2C-value of 3.57?±?0.36?pg. These 2C-values are within the range previously reported for Sphaeriidae (2.35–5.7?pg), which includes diploids and polyploids, amounting to 13 of the species examined around the world. Of the cytological data available for the family, the nuclear DNA content can have a unifying role in understanding the magnitude of the chromosome polymorphisms within this polyploid complex.     

The distribution and conservation of threatened Sphaeriidae on British grazing marshland

Freshwater sphaeriid bivalves are poorly known ecologically, particularly uncommon species such as Pisidium pseudosphaerium (UK RDB (Red Data Book) staus = ‘rare’). In the UK, this species occupies grazing marsh where conservation opportunities might be shared with other threatened molluscs. We surveyed sphaeriids including P. pseudosphaerium and snails in 106 drainage ditches in SE England in 1999. P. pseudosphaerium occupied over half the ditches surveyed, at slightly elevated BOD (6 ± 7 mg l⁻¹ sd) but reduced calcium (64 ± 31 mg l⁻¹) and nitrate (0.5 ± 1.2 mg l⁻¹). As part of a sphaeriid assemblage comprising Sphaerium corneum, Musculium lacustre and Pisidium obtusale (=Assemblage 1), P. pseudosphaerium occurred in ditches with floating vegetation and abundant snails of conservation importance, co-occurring significantly with either Valvata macrostoma (RDB ‘vulnerable’) or Anisus vorticulus (RDB: ‘vulnerable’). A more diverse sphaeriid assemblage (=Assemblage 2) included species common in wider, deeper ditches with open water. We suggest that traditional ditch management can support both rare and representative snails and bivalves on grazing marsh. Quasi-traditional and rotational ditch clearance will favour common sphaeriids and pioneer snails during early succession; P. pseudosphaerium, V. macrostoma, A. vorticulus during mid-succession; and the snail Segmentina nitida (RDB: ‘Endangered’) in late successional ditches. In common with threatened snails, P. pseudosphaerium will also benefit from reduced eutrophication. We recommend that P. pseudosphaerium retain RDB status to ensure protection and to emphasise the need for improved ecological information.     

Phylogeny of Veneridae (Bivalvia) based on mitochondrial genomes

Veneridae is one of the most diverse families of bivalve molluscs. However, their phylogenetic relationships among subfamilies have been debated for years. To explore phylogenetic relationships of Veneridae, we sequenced 13 complete mitochondrial genome sequences from eight subfamilies and compared with available complete mitochondrial genome of other Veneridae taxa (18 previously reported sequences). Phylogenetic analyses using probabilistic methods recovered two highly supported clades. In addition, the protein‐coding gene order revealed a highly conserved pattern among the same subclade lineages. According to our molecular analyses, Tapetinae should be recognized as a valid subfamily, but the genera formed para‐polyphyletic clades. Chioninae was recovered not monophyletic that differs from a previously molecular phylogeny. Furthermore, the reconstructed chronogram calibrated with fossils recovered the Veneridae have originated during the early Permian (about 290 million years ago). Noticeably, programmed frameshift was found in the nad4 gene of Leukoma jedoensis, Anomalodiscus squamosus and Antigona lamellaris and cob gene of L. jedoensis. This is the first time that the presence of the programmed frameshift has been found in the protein‐coding genes of Heterodonta species. Our results improved the phylogenetic resolution within Veneridae, and a more taxonomic sampling analysis of the subfamily Chioninae is supposed to construct.     

Complete mtDNA sequence of the North American freshwater mussel,Lampsilis ornata (Unionidae): an examination of the evolution and phylogenetic utility of mitochondrial genome organization in Bivalvia (Mollusca)

Molluscs in general, and bivalves in particular, exhibit an extraordinary degree of mitochondrial gene order variation when compared with other metazoans. Two factors inhibiting our understanding the evolution of gene rearrangement in bivalves are inadequate taxonomic sampling and failure to examine gene order in a phylogenetic framework. Here, we report the first complete nucleotide sequence (16,060 bp) of the mitochondrial (mt) genome of a North American freshwater bivalve, Lampsilis ornata (Mollusca: Paleoheterodonta: Unionidae). Gene order and mt genome content is examined in a comparative phylogenetic framework for Lampsilis and five other bivalves, representing five families. Mitochondrial genome content is shown to vary by gene duplication and loss among taxa and between male and female mitotypes within a species. Although mt gene arrangement is highly variable among bivalves, when optimized on an independently derived phylogenetic hypothesis, it allows for the reconstruction of ancestral gene order states and indicates the potential phylogenetic utility of the data. However, the interpretation of reconstructed ancestral gene order states must take in to account both the accuracy of the phylogenetic estimation and the probability of character state change across the topology, such as the presence/absence of atp8 in bivalve lineages. We discuss what role, if any, doubly uniparental inheritance (DUI) and recombination between sexual mitotypes may play in influencing gene rearrangement of the mt genome in some bivalve lineages.     

Inter-generic relationships of the crows, jays, magpies and allied groups (Aves: Corvidae) based on nucleotide sequence data

Phylogenetic relationships were studied based on DNA sequences obtained from all recognized genera of the family Corvidae sensu stricto . The aligned data set consists 2589 bp obtained from one mitochondrial and two nuclear genes. Maximum parsimony, maximum-likelihood, and Bayesian inference analyses were used to estimate phylogenetic relationships. The analyses were done for each gene separately, as well as for all genes combined. An analysis of a taxonomically expanded data set of cytochrome b sequences was performed in order to infer the phylogenetic positions of six genera for which nuclear genes could not be obtained. Monophyly of the Corvidae is supported by all analyses, as well as by the occurrence of a deletion of 16 bp in the β-fibrinogen intron in all ingroup taxa. Temnurus and Pyrrhocorax are placed as the sister group to all other corvids, while Cissa and Urocissa appear as the next clade inside them. Further up in the tree, two larger and well-supported clades of genera were recovered by the analyses. One has an entirely New World distribution (the New World jays), while the other includes mostly Eurasian (and one African) taxa. Outside these two major clades are Cyanopica and Perisoreus whose phylogenetic positions could not be determined by the present data. A biogeographic analysis of our data suggests that the Corvidae underwent an initial radiation in Southeast Asia. This is consistent with the observation that almost all basal clades in the phylogenetic tree consist of species adapted to tropical and subtropical forest habitats.     

Multi-gene phylogenies indicate ascomal wall morphology is a better predictor of phylogenetic relationships than ascospore morphology in the Sordariales (Ascomycota, Fungi)

Ascospore characters have commonly been used for distinguishing ascomycete taxa, while ascomal wall characters have received little attention. Although taxa in the Sordariales possess a wide range of variation in their ascomal walls and ascospores, genera have traditionally been delimited based on differences in their ascospore morphology. Phylogenetic relationships of multiple representatives from each of several genera representing the range in ascomal wall and ascospore morphologies in the Sordariales were estimated using partial nuclear DNA sequences from the 28S ribosomal large subunit (LSU), beta-tubulin, and ribosomal polymerase II subunit 2 (RPB2) genes. These genes also were compared for their utility in predicting phylogenetic relationships in this group of fungi. Maximum parsimony and Bayesian analyses conducted on separate and combined data sets indicate that ascospore morphology is extremely homoplastic and not useful for delimiting genera. Genera represented by more than one species were paraphyletic or polyphyletic in nearly all analyses; 17 species of Cercophora segregated into at least nine different clades, while six species of Podospora occurred in five clades in the LSU tree. However, taxa with similar ascomal wall morphologies clustered in five well-supported clades suggesting that ascomal wall morphology is a better indicator of generic relationships in certain clades in the Sordariales. The RPB2 gene possessed over twice the number of parsimony-informative characters than either the LSU or beta-tubulin gene and consequently, provided the most support for the greatest number of clades.     

The Evolutionary History of Sarco(endo)plasmic Calcium ATPase (SERCA)

Investigating the phylogenetic relationships within physiologically essential gene families across a broad range of taxa can reveal the key gene duplication events underlying their family expansion and is thus important to functional genomics studies. P-Type II ATPases represent a large family of ATP powered transporters that move ions across cellular membranes and includes Na⁺/K⁺ transporters, H⁺/K⁺ transporters, and plasma membrane Ca²⁺ pumps. Here, we examine the evolutionary history of one such transporter, the Sarco(endo)plasmic reticulum calcium ATPase (SERCA), which maintains calcium homeostasis in the cell by actively pumping Ca²⁺ into the sarco(endo)plasmic reticulum. Our protein-based phylogenetic analyses across Eukaryotes revealed two monophyletic clades of SERCA proteins, one containing animals, fungi, and plants, and the other consisting of plants and protists. Our analyses suggest that the three known SERCA proteins in vertebrates arose through two major gene duplication events after the divergence from tunicates, but before the separation of fishes and tetrapods. In plants, we recovered two SERCA clades, one being the sister group to Metazoa and the other to Apicomplexa clade, suggesting an ancient duplication in an early eukaryotic ancestor, followed by subsequent loss of one copy in Opisthokonta, the other in protists, and retention of both in plants. We also report relatively recent and independent gene duplication events within invertebrate taxa including tunicates and the leech Helobdella robusta. Thus, it appears that both ancient and recent gene duplication events have played an important role in the evolution of this ubiquitous gene family across the eukaryotic domain.     

Ancient allopolyploid speciation in Geinae (Rosaceae): evidence from nuclear granule-bound starch synthase (GBSSI) gene sequences

A nuclear low-copy gene phylogeny provides strong evidence for the hybrid origin of seven polyploid species in Geinae (Rosaceae). In a gene tree, alleles at homologous loci in an allopolyploid species are expected to be sisters to orthologues in the ancestral taxa rather than to each other. Alleles at a duplicated locus in an autopolyploid, however, are expected to be more closely related to each other than they are to any orthologous copies in closely related species. We cloned and sequenced about 1.9 kilobases from the 5' end of the GBSSI-1 gene from two diploid, one tetraploid, and six hexaploid species. Each of the three loci in the hexaploid species forms a separate group, two of which are more closely related to copies in other species than they are to each other. This finding indicates that the hexaploid lineage evolved through two consecutive allopolyploidization events. Based on the GBSSI-1 gene tree, we hypothesized that there was an initial hybridization between a diploid species from the ancestral lineage of Coluria and Waldsteinia and an unknown diploid species to form the tetraploid Geum heterocarpum lineage. Backcrossing of G. heterocarpum with a representative of the unknown diploid lineage then resulted in a hexaploid lineage that has radiated considerably since its origin, comprising at least 40 extant species with various morphologies. A penalized likelihood analysis indicated that Geinae may be about 17 million years old, implying that the hypothesized allopolyploid speciation events are relatively ancient. Six of the 22 cloned Geinae GBSSI-1 copies in this study, which all are duplicate copies in polyploid taxa, may have become pseudogenes. We compared the GBSSI-1 phylogeny with one from chloroplast data and explored implications for the evolution of some fruit characters.     

Consequences of genome duplication

Polyploidy has been widely appreciated as an important force in the evolution of plant genomes, but now it is recognized as a common phenomenon throughout eukaryotic evolution. Insight into this process has been gained by analyzing the plant, animal, fungal, and recently protozoan genomes that show evidence of whole genome duplication (a transient doubling of the entire gene repertoire of an organism). Moreover, comparative analyses are revealing the evolutionary processes that occur as multiple related genomes diverge from a shared polyploid ancestor, and in individual genomes that underwent several successive rounds of duplication. Recent research including laboratory studies on synthetic polyploids indicates that genome content and gene expression can change quickly after whole genome duplication and that cross-genome regulatory interactions are important. We have a growing understanding of the relationship between whole genome duplication and speciation. Further, recent studies are providing insights into why some gene pairs survive in duplicate, whereas others do not.     

Phylogenies from genetic and morphological characters do not support a revision of Gigasporaceae (Glomeromycota) into four families and five genera

The family Gigasporaceae consisted of the two genera Gigaspora and Scutellospora when first erected. In a recent revision of this classification, Scutellospora was divided into three families and four genera based on two main lines of evidence: (1) phylogenetic patterns of coevolving small and large rRNA genes and (2) morphology of spore germination shields. The rRNA trees were assumed to accurately reflect species evolution, and shield characters were selected because they correlated with gene trees. These characters then were used selectively to support gene trees and validate the classification. To test this new classification, a phylogenetic tree was reconstructed from concatenated 25S rRNA and β-tubulin gene sequences using 35% of known species in Gigasporaceae. A tree also was reconstructed from 23 morphological characters represented in 71% of known species. Results from both datasets showed that the revised classification was untenable. The classification also failed to accurately represent sister group relationships amongst higher taxa. Only two clades were fully resolved and congruent among datasets: Gigaspora and Racocetra (a clade consisting of species with spores having one inner germinal wall). Other clades were unresolved, which was attributed in part to undersampling of species. Topology of the morphology-based phylogeny was incongruent with gene evolution. Five shield characters were reduced to three, of which two were phylogenetically uninformative because they were homoplastic. Therefore, most taxa erected in the new classification are rejected. The classification is revised to restore the family Gigasporaceae, within which are the three genera Gigaspora, Racocetra, and Scutellospora. This classification does not reflect strict topology of either gene or morphological evolution. Further revisions must await sampling of additional characters and taxa to better ascertain congruence between datasets and infer a more accurate phylogeny of this important group of fungi.     

Evolution of the high molecular weight glutenin loci of the A, B, D, and G genomes of wheat.

We used PCR to obtain phylogenetically informative sequences from the high molecular weight glutenin genes of wheat. The validity of partial sequence comparisons as a means of studying glutenin phylogenetics was established by constructing neighbour-joining trees from partial alignments of 12 published glutenin allele sequences. PCR was then used to obtain 20 novel glutenin allele sequences from various Triticum and Aegilops species, including a 3000 year old preserved wheat. A neighbour-joining tree derived from all known glutenin allele sequences had eight clades, representing the eight loci from which the allele sequences were derived, and was split into two halves, one comprising alleles from the Glu-1-1 loci and the other comprising Glu-1-2 alleles. The topology was compatible with the postulated relationships between the A, B, D, and G genomes. The Glu gene duplication event was tentatively dated at 7.2-10.0 million years ago (MYA), the origin of the four genomes at 5.0-6.9 MYA, and the split between the B and G genomes at 2.5-3.5 MYA. The Glu-B1-1 alleles in cultivated wheats fell into two subgroups that diverged 1.4-2.0 MYA, suggesting that emmer was domesticated twice. The D allele sequences were relatively diverse, indicating that the hybridization event that resulted in the hexaploid bread wheats might have occurred more than once.     

Snake relationships revealed by slow-evolving proteins: a preliminary survey

We present an initial evaluation of relationships among a diverse sample of 215 species of snakes (8% of the world snake fauna) representing nine of the 16 commonly-recognized families. Allelic variation at four slow-evolving. protein-coding loci, detected by starch-gel electrophoresis, was found to be informative for estimating relationships among these species at several levels. The numerous alleles detected at these loci [ Arp -2 (42 alleles). Ltlh -2 (43), Mdh -1 (29), Pgm (Z)] provided unexpected clarity in partitioning these taxa. Most congeneric species and several closely-related genera have the same allele at all four loci or differ at only a single locus. At thc other extreme are those species with three or four unique alleles; these taxa cannot be placed in this analysis. Species sharing two or three distinctive alleles are those most clearly separated into clades. Typhlopids, pythonids, viperids, and elapids were resolved into individual clades. whereas bods were separated into boincs and erycines, and colubrids appeared as scveral distinct clades (colubrines, natricines, psammophines, homalopsines, and xenodontines). Viperids were recognized as a major division containing three separate clades: Asian and American crotalines. Pabearctic and Oriental viperines, and Ethiopian causines. The typhlopids were found to be the basal clade, with the North American erycine boid Chrrrino and the West Indian woodsnakes Tropidophi, Y near the base. A number of species and some small clades were not allocated because of uninformative (common, unique, or conflicting) alleles. Of the 21 S species examined, five to eight appear to have been misplaced in the analysis of these electrophoretic data.     

Polymorphism of visual pigment genes in the muriqui (Primates, Atelidae)

Colour vision varies within the family Atelidae (Primates, Platyrrhini), which consists of four genera with the following cladistic relationship: {Alouatta[Ateles (Lagothrix and Brachyteles)]}. Spider monkeys (Ateles) and woolly monkeys (Lagothrix) are characteristic of platyrrhine monkeys in possessing a colour vision polymorphism. The polymorphism results from allelic variation of the single-locus middle-to-long wavelength (M/L) cone opsin gene on the X-chromosome. The presence in the population of alleles coding for different M/L photopigments results in a variety of colour vision phenotypes. Such a polymorphism is absent in howling monkeys (Alouatta), which, alone among platyrrhines, acquired uniform trichromatic vision similar to that of Old World monkeys, apes, and humans through opsin gene duplication. Dietary and morphological similarities between howling monkeys and muriquis (Brachyteles) raise the possibility that the two genera share a similar form of colour vision, uniform trichromacy. Yet parsimony predicts that the colour vision of Brachyteles will resemble the polymorphism present in Lagothrix and Ateles. Here we test this assumption. We obtained DNA from the blood or faeces of 18 muriquis and sequenced exons 3 and 5 of the M/L opsin gene. Our results affirm the existence of a single M/L cone opsin gene in the genus Brachyteles. We detected three alleles with predicted lambdamax values of 530, 550, and 562 nm. Two females were heterozygous and are thus predicted to have different types of M/L cone pigment. We discuss the implication of this result towards understanding the evolutionary ecology of trichromatic vision.